The invention relates to a receiver for a passband signal generated by phase-shift keying of a carrier in accordance with a data signal of a predetermined symbol rate 1/T, the receiver comprising:
demodulation means for demodulating the received passband signal with the aid of a local carrier and thereby producing a demodulated data signal;
regeneration means for regenerating the demodulated data signal with the aid of a local clock and thereby producing a regenerated data signal;
carrier recovery means having a local carrier generator included in a phase-locked loop and connected to the demodulation means, and having a remodulator for phase-shift keying of the received passband signal in accordance with the regenerated data signal and thereby producing a carrier component as an input signal for the phase-locked loop; and
a local clock generator connected to the regeneration means.
A receiver having such a structure is known from the second edition of the book "Phase Lock Techniques" by F. M. Gardner, Wiley, New York, 1979, Chapter 11, Section 11.2, pp. 216-230.
For data transmission with the aid of phase-shift keying (PSK) of a carrier, a first requirement for an optimum detection of the data signal is the availability of a stable local carrier with little phase jitter in the receiver to enable coherent demodulation of the received modulation band signal (PSK-signal). A known method to obtain this local carrier utilizes the principle of PSK-remodulating the received PSK-signal in accordance with the demodulated data signal for producing a carrier component that is used as an input signal for a phase-locked loop (PLL) in which a local carrier generator is included (cf. FIGS. 11.4, 11.5 and 11.8 on pp. 219, 220 and 223 of the above-mentioned book by Gardner). In applications of the receiver in systems in which the available signal power is limited and the channel properties are unfavorable, as in the case in systems for satellite communication and systems for mobile communication, the signal-to-noise ratio (SNR) at the input of the receiver can assume relatively low values. In these circumstances, the PSK-remodulation should preferably be performed by using the data signal regenerated as regards amplitude and instant of occurrence instead of the demodulated data signal itself, as the improvement in noise suppression results in a reliable recovery of the carrier at lower SNR-values at the input of the receiver. True enough, the error probability of the received data symbols becomes indeed greater at these lower SNR-values, but the influence of the increased error probability can effectively be combated by the use of error-correcting codes as long as the receiver provides for a reliably recovered carrier. A requirement to achieve this improvement in the transmission quality is that the receiver provides, also at these lower SNR-values, a stable local clock with little phase jitter. When use is made of the known methods for recovering the local clock from the demodulated data signal, as described in Section 11.3, pp. 230-249 of said book by Gardner, there is however the disadvantage that the generation of a clock component as an input signal for a phase-locked loop including the local clock generator, generally requires operations which result in the introduction of additional noise in the control signal for the local clock generator. This is more specifically the case with operations such as rectifying, squaring or limiting, which are based on the use of elements having a non-linear amplitude transfer characteristic. The additional noise thus introduced implies that higher SNR-values are required at the input of the receiver so as to be able to ensure a reliable clock recovery.